The principle of injection molding is apparently simple: Melted polymer is used to fill up a mold for the fabrication of a part. In reality, it is a complex process with many parameters. The basic process is: 1) injection of liquid polymer into the mold 2) cooling so the polymer solidifies, and 3) de-molding of the part. An injection molding machine converts thermoplastic granular or pellets into finished parts.
An injection mold is also known as a molding tool, and typically it has an exchangeable mold cavity. This prolongs the tool life, since only the cavity need replacement when the mold cavity is worn out.
Nanostructures may already be injection molded on 2D surfaces e.g. in the production of Blu-ray disc and DVDs. However, the current structure size limit for so-called freeform injection molding is approximately 50 μm. Free form surfaces are generally designed using computer aided design (CAD) techniques, and are usually not bound by rigid radial coordinates like planes, cylinders, conic surfaces, etc. Thus, there is a need for a more advanced injection molding techniques capable of molding constructional details below the effective 50 μm limit.
WO 2009/028745 (to LG Electronic Inc.) discloses an injection-molding apparatus. The injection-molding apparatus comprises: a mold having a cavity; a core mold having a core surface to form a molding space for injection moldings when being joined to the cavity mold; a heating unit for heating the cavity mold or the core mold; a cooling unit for cooling the cavity mold or the core mold; and a patterning stamp having a micrometer or nanometer sized pattern and provided on an inner surface of the molding space. A micrometer or nanometer sized pattern is formed on a surface of injection moldings so as to have a super-hydrophobic characteristic and an optical characteristic, and a micrometer or nanometer sized pattern of a complex structure can be implemented by placing the patterning stamp inside the mold cavity.
However, this molding apparatus is inherently limited to patterning stamps that are prepared outside of the molding apparatus, and subsequently inserted into the dedicated position within the molding tool and is limited to micro- and nanometer patterning of planar or simple curved surfaces (bend planes like cylinders). This, in turn, also limits the available forms that are possible to pattern because of the high pressure and/or high temperature in an injection molding system when molding. Thus, more complex forms are not easily patterned by this method. Accordingly, the disclosed method is rather inflexible due to limited forms available.
Hence, an improved injection molding tool would be advantageous, and in particular a more efficient and/or reliable molding tool would be advantageous.